JPH0389154A - Dissolved gas sensor and forming method of groove of the same sensor - Google Patents

Abstract

PURPOSE:To realize a sensor with quick response speed and long life by arranging a gas electrode and a gas permeable film adjacent to each other. CONSTITUTION:A groove 2 is formed in a Si substrate 1. An oxide film 3 is coated on the surface of the substrate 1 including the inside of the groove 2. An electrode supporting body 5 made of an oxide film is provided above the groove 2, with a Pt electrode 6 thereon. Moreover, an Ag/AgCl electrode 4 is provided at the lateral face of the groove 2. An Si3N4 film 11 is formed on the oxide film 3 where the groove 2 is not present thereby to protect the electrode from a solution to be measured. A polyimide film 7 is laminated above the oxide film 3. An internal electrolytic gel 12 is filled in the groove 2, above which a gas permeable film 8 is formed. Then, the electrodes 6 and 4 are provided with a cathode terminal 9 and an anode terminal 10, respectively, to be connected to an outside measuring circuit. In this structure, since the electrodes are provided adjacent to the gas permeable film, the scattering distance of gas from the permeable film is shortened and the response speed is improved. Moreover, the volume of the electrolytic gel 12 is increased per area of the sensor, accordingly elongating the service life of the sensor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a dissolved gas sensor used in clinical tests and environmental measurements, and in particular to a sensor for measuring the partial pressure or concentration of oxygen or carbon dioxide dissolved in blood, river water, etc. The present invention relates to a dissolved gas sensor suitable for measuring.

[Conventional technology]

Conventionally, small dissolved oxygen sensors using semiconductor substrates have been described in Proceedings of the Third Sensor Symposium (1983), pages 21 to 26 (Proceedings of the Third Sensor Symposium (1983), pages 21 to 26).
edings of The 3rd sensorS
ymposium (1983) PP 21-26). This dissolved oxygen sensor has a groove formed by anisotropic etching, an electrode pair placed in the groove, and a Teflon gas permeable membrane placed above the groove.
This gas permeable membrane is configured to retain the internal electrolyte gel within the groove.

Dissolved carbon dioxide sensors are discussed in "Medical Electronics and Bioengineering", Vol. 19, Special Issue (1981), page 28. This dissolved carbon dioxide sensor is a pH-responsive ion-sensitive field-effect transistor (hereinafter referred to as
It has a structure in which A g /A g Cn electrodes are formed on a 15FET), a silicon tube is used as a gas permeable membrane, and an electrolyte gel is wrapped in the upper part of the 15FET.

[Problem to be solved by the invention]

However, in the conventional dissolved oxygen sensor described above.

The gas permeable membrane and the frame for holding the gas permeable membrane are manufactured separately and assembled together. The internal electrolyte gel is also injected separately. For this reason, in manufacturing the dissolved oxygen sensor, although a semiconductor substrate is used, it is difficult to match it with a semiconductor process.

In addition, in conventional dissolved carbon dioxide sensors, the internal electrolyte gel is held in a silicon tube, so the gas permeable membrane and pH
It is difficult to maintain a constant distance from the sensitive part of the 15FET, and unless the capacity of the internal electrolyte gel is increased to extend the sensor life, the above distance will become longer and the response speed will become slower. There's a problem. For this reason,
Conventional dissolved carbon dioxide sensors generally have large variations in response characteristics between sensors.

An object of the present invention is to provide a dissolved gas sensor that has good compatibility with semiconductor processes so that it can be consistently formed on a sensor substrate, has a fast response speed, and has small variations in sensor characteristics.

[Means to solve the problem]

In order to achieve the above object, the present invention forms a groove on a semiconductor substrate, provides an electrode support at the top or middle part of the groove, and a metal electrode on the electrode support, and a side surface of the groove. Alternatively, a reference electrode such as A g / A g CQ is provided at the bottom, and an internal electrolyte gel is filled in the groove, and the filled internal electrolyte gel is covered with a gas permeable membrane. shall be.

The present invention also provides a method for forming a groove on a semiconductor substrate, providing an electrode support at the top or middle of the groove, and disposing a metal/metal oxide film electrode on the electrode support at the side or bottom of the groove. In addition to disposing reference electrodes such as A g / A g CQ, respectively, and filling the groove with an internal electrolyte gel,
It is characterized by covering the filled internal electrolyte gel with a gas permeable membrane.

The present invention also provides a method for forming a groove on a semiconductor substrate, providing an electrode support at the top or middle of the groove, and disposing a metal/metal oxide film electrode on the electrode support at the side or bottom of the groove. In addition to disposing reference electrodes such as Ag/AgCl, the grooves are filled with an internal electrolyte gel, and the filled internal electrolyte gel is covered with a gas permeable membrane, and the metal/metal oxide membrane electrode is It is characterized in that one end is connected to a metal gate field effect transistor provided on the semiconductor substrate.

Further, in the present invention, the dissolved gas sensor is housed on one side of the catheter tube, and a hole is provided on one side of the catheter tube for the gas sensitive part of the dissolved gas sensor to come into contact with the solution to be measured, and the dissolved gas sensor The present invention is characterized in that a connector for electrically connecting the gas sensor to the outside is provided on the other side of the catheter tube.

Further, the present invention uses silicon with a crystal axis <100> as a semiconductor substrate, and a film body made of a material different from silicon, such as an oxide film or a silicon nitride film, is laminated on the surface of the semiconductor substrate, and an electrode is supported on the laminated film body. The method is characterized in that after the groove portion is etched leaving the body pattern, the groove is formed in the semiconductor substrate including the lower part of the electrode support by anisotropic etching.

[Effect]

According to the above configuration, the groove-shaped electrode support allows the metal electrode or the metal/metal oxide film electrode to be brought close to the gas permeable membrane, thereby shortening the gas diffusion distance from the gas permeable membrane. , the response speed of the dissolved gas sensor can be improved.

In addition, one end of the metal/metal oxide film electrode is connected to a metal gate field effect transistor (hereinafter referred to as MOS) on the same sensor substrate.
By connecting to a metal/metal oxide film electrode, the output impedance of a single metal/metal oxide film electrode is high in pH response and easily generates noise due to disturbance, but by impedance conversion of the 1M08 FET, the output impedance can be reduced to a low value.

As a result, even if the dissolved gas sensor is miniaturized, it is possible to obtain a signal that is less susceptible to noise and has a high S/N ratio.

Furthermore, if the above-described dissolved gas sensor is housed in a catheter tube to form a probe-like dissolved gas sensor, it can be easily inserted into a blood vessel or the like, and carbon dioxide gas or the like in the blood can be easily detected.

In addition, by anisotropic etching, Si with crystal axis <100>
When etched, a <111> plane is left behind, so the etching design pattern is etched only in the depth direction without being etched in the lateral direction, resulting in a groove as designed and improved reproducibility of the sensor shape. , variations in characteristics between sensors are reduced. At the same time, the lower part of the electrode support can be etched by anisotropic etching, so the capacity of the internal electrolyte gel filled in the groove can be increased relative to the sensor area. This makes it possible to extend the sensor life.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

(First Example) First, FIG. 1 shows an overview of a dissolved oxygen sensor that is a first example of the present invention, and FIG.
Each is shown in the figure. As shown in the figure, a groove 2 is formed in a sensor substrate 1 made of Si, and the surface of the sensor substrate 1 including the inside of the groove 2 is covered with an oxide film 3. An electrode support 5 made of an oxide film 3 is formed above the groove 2, and a PT electrode 6 is placed on the electrode support 5. An A g /A g CQ electrode 4 is arranged on the side surface of the groove 2 . In addition, Si, N4 film 1 is formed on the oxide film 3 on the part other than the groove 2.
1 is formed to protect the electrode from the solution to be measured. Furthermore, a polyimide film 7 is laminated on top of the oxide film 3. The groove 2 is filled with an internal electrolyte gel 12, and a gas permeable membrane 8 is formed above the internal electrolyte gel 12.

Further, the Pt electrode 6 is provided with a cathode terminal 9, and the Ag/AgCl electrode 4 is provided with an anode terminal 10, respectively, and can be connected to an external measurement circuit via these terminals 9 and 10.

Such a dissolved oxygen sensor is manufactured as follows.

First, using Si with a crystal axis (100>) as a sensor substrate 1, a groove 2 is formed in the sensing portion at the tip of the sensor by anisotropic etching with a KOH aqueous solution.

After forming the groove 2 on the sensor substrate 1, oxidation treatment is performed to form an oxide film 3 on the surface of the sensor substrate 1. Then, an A g /A g CQ electrode 4 is formed on the side surface of the groove 2 . An electrode support 5 is formed on the top of the groove 2 using the oxide film 3 left behind when forming the groove, and a Pt electrode 6 is formed on this. Pt
A cathode terminal 9 is connected to the electrode 6, and an anode terminal 10 is connected to the A g /A g CQ electrode 4, respectively. Prepare an electrolyte solution by dissolving KCQ in phosphate buffer, and insert internal electrolyte gel 12 mixed with polyvinyl alcohol (PVA) into groove 2.
Fill inside. A polyimide film 7 is formed so as to open the upper part of the groove 2, and a gas permeable film 8 made of silicon is formed in the opening.

Figure 3 shows the experimental results of investigating the response characteristics using the dissolved oxygen sensor of this example.
It can be seen that a nearly linear response is obtained in the range of 800 m Hg. Figure 4 shows the gas permeable membrane 8 in this sensor.
The results of an experiment in which the sensor response time was investigated by changing the distance between the 0 interval and the electrode support 5 are shown.Response time becomes extremely poor when the 0 interval is removed.6If the interval is within 10μ, the response time is is within 1 minute. In this sensor, it is easy to bring the electrode support 5 and the gas permeable membrane 8 close to each other in this way, so that a quick response time can be obtained.

Note that the electrode support 5 may be provided not only at the top of the groove 2 but also in the middle of the groove 2, and the electrode support 5 may be supported not only from one side of the groove 2 but also from both sides of the groove 2. . A so-called bridging shape may also be used.

Also, instead of the Pt electrode 6, gold or iridium is used.

The same effect can be obtained by using an electrode made of any metal such as indium.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. 5 and 6. This sensor is a dissolved carbon dioxide sensor, and the basic structure of the sensor is similar to that of the first embodiment. The difference is in the electrode portion, in that a metal/metal oxide film electrode is formed on the electrode support 5. The metal/metal oxide film electrode has a structure in which platinum 6 is used as the metal and an iridium oxide film 13 is laminated thereon as the metal oxide film. This metal/metal oxide film electrode can be used as a pH sensor.

The principle of measuring carbon dioxide gas is based on the fact that dissolved carbon dioxide gas diffuses from the solution to be measured, and the pH of internal electrolyte gel 12 filled in groove 2 changes. By capturing this pH change, the dissolved carbon dioxide concentration in the solution to be measured can be measured. Here, the internal electrolyte gel 2 contains NaCQ and Na
A gel made by dissolving polyvinyl alcohol in an electrolyte solution containing HC○ is used.

Figure 7 shows the response results to the partial pressure of carbon dioxide gas.

It can be seen that a linear response is obtained with respect to the logarithm of the gas partial pressure.

In addition to platinum, the metals used for the metal/metal oxide film electrodes include gold, silver, palladium, and stainless steel.

In addition to iridium, platinum, palladium, and stainless steel are used as metal oxide films.

Indium can be used respectively.

(Third Embodiment) The third embodiment of the present invention will be explained with reference to FIG. 8. The six sensors are dissolved carbon dioxide sensors, and one end of the metal/metal oxide film electrode in the second embodiment is mounted on the same semiconductor substrate as the sensor. It is connected to the gate 14 of a field effect transistor (MOSFET) formed in the above. A change in the potential of the metal/metal oxide film electrode results in a change in the gate potential of the MOSFET, resulting in a change in the gate potential of the MOSFET. causing a current change between sources 16; The dissolved carbon dioxide partial pressure can be measured based on this amount of change. Furthermore, since the impedance of the sensor output can be lowered using MOSFET, noise is less likely to enter, and an inexpensive external measurement circuit with low input impedance can be used.

Figure 9 shows the gas partial pressure from 2 Q an Hg to 40 mmH.
It shows the time response when changing to g. Curve A is MOSFE
According to the second embodiment without connection to T, curve B is MOS
These are the results of a dissolved carbon dioxide sensor connected to an FET. A
In this case, the 95% response time is 1 minute 35 seconds and the noise level is 1.7.
mV, but in B, the response time is 40 seconds and the noise level is 0.4 mV. These results show that this example can realize a low-noise dissolved carbon dioxide sensor.

(Fourth Example) A fourth example according to the present invention will be described with reference to FIG. The figure shows a dissolved gas sensor 18 attached to a nylon tube 17 (1 mmφ). A tube opening 19 is provided on the side surface of the tube to expose the sensitive part 20 of the dissolved gas sensor. The solution to be measured comes into contact with the sensitive section 20 through the tube opening 19, and the dissolved gas concentration can be measured. The sensor output is measured by an external measurement circuit via a connector 22 through a lead wire 21 in the tube.

FIG. 11 shows the results of an experiment in which the sensor was inserted into a dog's artery and the partial pressure of carbon dioxide gas dissolved in the blood was investigated when the breathing rate was changed using a ventilator. The experimental results show that this sensor can continuously monitor the partial pressure of carbon dioxide in blood vessels.

〔Effect of the invention〕

As explained above, according to the present invention, the gas electrode and the gas permeable membrane can be placed close to each other, and the internal electrolyte gel capacity can be effectively increased per sensor area, so the dissolved gas sensor has a fast response speed and a long life. can be realized.

In addition, due to anisotropic etching, the design pattern for etching is hardly etched in the lateral direction, but can be etched only in the depth direction, which improves the reproducibility of the shape of the dissolved gas sensor during manufacturing and reduces the variation in characteristics between sensors. can be reduced.

Further, by forming a MOSFET on the sensor substrate, the impedance of the sensor output can be lowered, so a low-noise dissolved gas sensor can be realized.

Furthermore, by attaching the sensor to a catheter tube so that only the sensitive part of the sensor is exposed, continuous measurement inside a blood vessel or the like becomes possible.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a dissolved oxygen sensor according to the first embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig.
The figure is a diagram showing the calibration curve of a dissolved oxygen sensor, Figure 4 is a diagram showing the relationship between the distance between the electrode support and the gas permeable membrane and the response time in the dissolved oxygen sensor, and Figure 5 is a diagram showing the relationship between the response time and the distance between the electrode support and the gas permeable membrane in the dissolved oxygen sensor. 6 is a cross-sectional view taken along line VI-VI in FIG. 5, FIG. 7 is a diagram showing the calibration curve of the dissolved carbon dioxide sensor, and FIG. 10 is a conceptual diagram of a dissolved carbon dioxide sensor integrating MOSFET, which is the third embodiment of the present invention, FIG. 9 is a response curve diagram of the dissolved carbon dioxide sensor, and FIG. A conceptual diagram of the dissolved carbon dioxide sensor, and FIG. 11 is a response curve diagram of the dissolved carbon dioxide sensor. l...sensor substrate, 2...groove, 3...oxide film, 4
... A g / A g CQ electrode, 5... Electrode support, 6... PT electrode, 7... Polyimide membrane, 8...
... Gas permeable membrane, 9... Cathode terminal, 10... Anode terminal, 11... Si, N4 membrane, 12... Internal electrolyte gel, 13... Iridium oxide film, 14... Gate , 15
...Drain, 16...Source, 17...Nylon tube, 18...Dissolved gas sensor, 19...Tube opening, 20...Sensitive part. 21...Lead wire, 22...Connector.

Claims (1)

[Claims] 1. A groove is formed on a semiconductor substrate, an electrode support is provided at the top or middle part of the groove, a metal electrode is provided on the electrode support, and an Ag layer is provided on the side or bottom of the groove. A dissolved gas sensor, characterized in that reference electrodes such as /AgCl and the like are respectively disposed, an internal electrolyte gel is filled in the groove, and the filled internal electrolyte gel is covered with a gas permeable membrane. 2. The dissolved gas sensor according to claim 1, wherein the metal electrode is made of platinum, gold, iridium, or indium. 3. A groove is formed on the semiconductor substrate, an electrode support is provided at the top or middle part of the groove, a metal/metal oxide film electrode is provided on the electrode support, and an Ag/Ag film is provided on the side or bottom of the groove.
A dissolved gas sensor characterized in that reference electrodes such as Cl are provided, an internal electrolyte gel is filled in the grooves, and the filled internal electrolyte gel is covered with a gas permeable membrane. 4. In the dissolved gas sensor according to claim 3, the metal/metal oxide film electrode is formed of platinum, palladium, stainless steel, iridium, or indium on any one of platinum, gold, silver, palladium, stainless steel, iridium, and indium. A dissolved gas sensor comprising a stack of metal oxide films. 5. The dissolved gas sensor according to claim 1 or 3, wherein the electrode support is supported in a cantilever manner on one side of the groove. 6. The dissolved gas sensor according to claim 1 or 3, wherein the electrode support is supported across both sides of the groove. 7. A groove is formed on the semiconductor substrate, an electrode support is provided at the top or middle of the groove, a metal/metal oxide film electrode is provided on the electrode support, and an Ag/Ag film is provided on the side or bottom of the groove.
Reference electrodes such as Cl are provided respectively, and the grooves are filled with an internal electrolyte gel, and the filled internal electrolyte gel is covered with a gas permeable membrane, and one end of the metal/metal oxide film electrode is connected to the A dissolved gas sensor characterized in that it is connected to a metal gate field effect transistor provided on a semiconductor substrate. 8. The dissolved gas sensor according to claim 1, 3 or 7 is housed on one side of the catheter tube, and a hole is provided on one side of the catheter tube for the gas sensitive part of the dissolved gas sensor to come into contact with the solution to be measured. A probe-shaped dissolved gas sensor, further comprising a connector on the other side of the catheter tube for electrically connecting the dissolved gas sensor to the outside. 9. Using silicon with crystal axis <100> as a semiconductor substrate, laminating a film body made of a material different from silicon, such as an oxide film or a silicon nitride film, on the surface of the semiconductor substrate, and forming an electrode support pattern on the laminated film body. A method for forming a groove in a dissolved gas sensor, comprising: etching a groove portion, and then forming a groove in the semiconductor substrate including a lower portion of the electrode support by anisotropic etching.